1. Field of the Invention
The present invention generally relates to simplified electronic-free continuously variable transmission (CVT) control arrangements that control pressurizing and providing variable pressure control of a hydraulic system in a belt or chain drive CVT.
2. Description of the Related Art
A typical vehicle CVT comprises two V shaped pulleys and a steel chain or belt disposed between them. The chain or belt transfers power from one pulley to the other pulley during pulley rotation. Both pulleys are capable of axial displacement of a belt track in order to change the ratio of the vehicle drive line. The pulleys usually are hydraulically actuated for ratio changing by integral hydraulic cylinders, which also supply a variable clamping force on the chain. The clamping force is modulated, depending on the torque load, to reduce the likelihood of chain slippage under high torque conditions but without applying unnecessary force that would increase the chain wear at low torque conditions.
Many CVT control systems are in existence and in use around the world that satisfy the above-described functions. These generally are computer-controlled systems that gather information from engine and driveline sensors, including the driver actuated throttle position. This information is used to control the ratio changing and chain clamping forces by selective manipulation of the hydraulic system pressures. These systems are complex and feature many components that increase the cost of manufacture.